Based on the in-depth views of 20 senior UK insurance executives, the report Brexit: the insurers speak stated this was because businesses could start to relocate from the UK within one or two years of a Brexit vote, with some executives suggesting relocations “within weeks”.

Commissioned by law firm Kennedys, the study found all but one supported the UK remaining in Europe.

In addition, a ‘leave’ vote could affect insurers’ efforts to attract and retain talent from around Europe, but could also relieve pressure on the UK to limit non-EU migration.

“This could make it easier to recruit from the rest of the world,” said the firm.

It also reported that uncertainty of renegotiating a new settlement was the biggest concern for senior executives. Respondents believed that this would take at least five years to achieve.

“The firms we spoke to repeatedly said that there were too many unknowns for them to predict accurately the long-term impact of a Brexit on either themselves or the wider UK economy,” said the law firm.

Kennedys added that in the short term, firms expected the immediate impact to be on sterling, credit spreads and interest rates. Additionally, over the few years following a Brexit, there could be “downward pressure on employment, output and ultimately GDP growth”.

Citing from the official Brexit campaign Vote Leave, the report said EU regulation currently costs UK businesses more than £600m every week.

However, respondents dismissed these figures arguing that a UK-led regulatory regime would be just as robust as the current EU-led regime.

It was felt that even if it left the EU, the UK would still need to follow broadly equivalent regulations in order to negotiate maintenance of market access.

Nick Thomas, senior partner at Kennedys, said: “We created this report not to suggest to anyone how they should vote, but to identify the issues that will arise for business leaders in the insurance industry to resolve in the event of a ‘remain’ vote, and those to be addressed in the event of a ‘leave’ vote.

“That our research found widespread support for continued EU membership among insurance industry leaders is clear.”